<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>complex</title>
</head>
<body>
    <div id="app">
        <div class="input-num">
            <button @click="sub">-</button>
            <span>{{ num }}</span>
            <button @click="add">+</button>
        </div>
    </div>
    <script src="https://cdn.jsdelivr.net/npm/vue@2/dist/vue.js"></script>
    <script>
        var app = new Vue({
            el:'#app',
            data:{
                num:1
            },
            methods:{
                add:function () {
                    if (this.num<10){
                        this.num++;
                    }else {
                        alert('no add');
                    }
                },
                sub:function () {
                    if (this.num>0){
                        this.num--;
                    }else {
                        alert('no sub');
                    }
                }
            }
        })
    </script>

</body>
</html>